The overall objectives of these studies are to: (1) Use current and develop new assay methods for erythropoietin, the hormone that stimulates the formation of red blood cells; (2) identify the site of production and action of erythropoietin; and (3) assess the role of hematopoietic control mechanisms in pregnancy, uremia and cyclic hematopiesis. During the next grant year it is planned to (1) evaluate new methods of performing the fetal mouse liver cell assay; (2) continue the production of antibodies to erythropoitin with the goal of producing a monospecific antiserum; (3) develop a method of assessing production of the putative poietincontrolling factors in cyclic hematopoietic dogs as well as studying the hematopoietic stimulating and inhibiting factors produced by cyclic hematopoietic dog bone marrow cells; and (4) continue to work on developing an immunoradiometric assay for erythropoietin.